Our planet's magnetic field periodically flips its direction, with the magnetic North and South Poles switching places. Such a reversal could wreak havoc on human society — and there's now reason to think one could happen soon... in geological terms, at least.

If nothing else, it's been an unusually long period since the last reversal — the geological evidence suggests the field flips about once every 450,000 years, and it's been about 780,000 years since the last reversal. That in itself doesn't necessarily mean a reversal is imminent, as there have been past instances where a million years passed from one reversal to the next. Just over 200,000 years may not be much time as far as the planet is concerned, but it would mean the chances of humanity having to deal with a magnetic field reversal in even the long-term future remain extremely low.

To have any idea of when a reversal might occur, we first need to know more about the mechanism that causes it, and that's where new research by Peter Olson and Renaud Deguen of Johns Hopkins enters the picture. Their seismic imaging of Earth's core revealed lopsided growth — in other words, the core wasn't spherical or even all that close to it, with one hemisphere slowly melting into something noticeably smaller than the other half. Currently, the eastern hemisphere of the core is bigger than its western counterpart.

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This lines up neatly with the current location of the axis of Earth's magnetic field. The line linking the two magnetic poles doesn't pass right through the center of the Earth, but is in fact offset about 300 miles eastward. Their data suggests this is a change from recent history, as until about 200 years ago the magnetic axis was solidly in the western hemisphere for at least 10,000 years. In what is likely not a coincidence, it was about two centuries ago that the inner core's eastern hemisphere started growing bigger.

All this indicates some fairly rapid movement from west to east, and Olson and Deguen's research indicates a link between these sorts of quick shifts and magnetic field reversals in the past. This might be enough to suggest that a magnetic reversal is already underway, although the researchers are quick to point out that the core is simply too chaotic to say anything with certainty at this stage. It's only a possibility, perhaps a very remote one, but this new model at least suggests that it is a possibility.

Besides, reversals take anywhere from 1,000 to 10,000 years — even if you do want to grant that we're two centuries into one, that doesn't necessarily mean its more serious effects on human technology will be felt in the next few centuries, let alone in our lifetimes. This is the problem with being in the middle of a geological event — they're so damn slow it's hard to tell if anything is actually happening at all.